1. Field of the Invention
The present invention relates to a flat-object holder for use in holding , semiconductor wafers or other thin, flat objects, and to a method of using such flat-object holders.
2. Related Arts
Referring to FIG. 27, a semiconductor wafer W1 has a plurality of ICs, LSIs or other circuits formed thereon, and it has a protection tape T applied to its front side for protecting the circuits. The semiconductor wafer W1 is put on a chuck table 70 with its protection tape directed down, thereby permitting the rear side of the semiconductor wafer to be ground with a grindstone 71 until a predetermined thickness has been reached. To meet the recent tendency of reducing the size and weight of cellular phones, notebook-sized personal computers and other electronic devices, it is required that parts of such devices be down-sized accorcingly, and semiconductor wafers need to be ground until their thickness is 100 or less μm thick, or 50 or less μm thick.
If semiconductor wafers are ground to be 200 to 400 μm thick, they are thick and strong enough to facilitate their transfer in the grinding apparatus or insertion in containers without fear of their being broken. However, semiconductor wafers whose thickness is reduced to be 50 to 100 μm cannot be transferred with ease because of their fragility.
Referring to FIG. 28, a semiconductor wafer W2 has grooves 72 made in the form of a lattice on its front side, each groove being deep enough to be equal to the thickness of each of the semiconductor chips, into which the semiconductor wafer W2 is to be diced. The semiconductor wafer W2 is ground on its rear side until the grooves 72 appear on the rear side to divide the semiconductor wafer into squares. This is called a “pre-dicing” method. Such square pieces, however, are too fragile to hold their appearance free of any defects.
In an attempt to avoid such inconvenience, protection tapes of good strength, for instance, made of polyethylene terephthalate are applied to semiconductor wafers. Such reinforced semiconductor wafers or chips can be transferred or put in containers without fear of breaking. Disadvantageously, such protection tapes cannot be peeled off the semiconductor wafers or chips without difficulty.
Referring to FIG. 29, a semiconductor wafer W is fixedly held by an annular frame F with the aid of an adhesive protection tape T to be convenient for dicing. Such wafer-and-frame assemblies are convenient for handling in transport or for putting in containers, and the protection tapes can be removed from the thin wafers or chips with ease. Disadvantageously the grinding machine needs to be modified so that its chuck table may hold the wafer-and-frame assembly.
In view of the above, there has been a demand for handling fragile flat objects such as semiconductor wafers easily when transporting; permitting the chuck table to hold such fragile flat objects without the necessity of redesigning the chuck table; and removing semiconductor wafers from their protection tapes with ease after being grounded.